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Hello, here's my beta reading feedback:
 let's cut the crap. Here's the thing: you've got a solid skeleton here. The bones are good boy and his horse, magic master, instant action. But right now, it reads like you're telling me a movie instead of dropping me inside one. I'm not feeling the sand under my feet or the panic in his chest. Let's fix that.
Here’s my line-by-line, gut-instinct feedback. I'm keeping every single event you wrote, just twisting the prose so it breathes.
The ocean was cursed. Watery sirens lurked, and a horde of them swam toward a dark, tropical island. The ocean water glistened in the moonlight, giving it a mysterious feel.
This first paragraph is your handshake with the reader. Right now, it's a limp fish. You're telling me it's cursed, then explaining it. Kill the explanation. Make me feel the curse.
Try this: The ocean was cursed. Everyone knew it. But tonight, under that fat, silver moon, the water looked almost peaceful which was the worst part. Because just beneath that glistening surface, a horde of watery sirens swam hard for the dark island, and they were hungry.
See the difference? We're in a point of view now. Someone knows something bad is coming.
The sirens crept closer to the island, but were unaware that somebody on it was ready for their arrival.
This is fine, but it's a narrator robot. Let's get inside the head of the "somebody."
Try this: They had no idea what was waiting for them on the beach.
Short. Threatening. Boom.
Two shadowy figures of a horse and a boy stood on the beach, and they watched the incoming beasts together.
The boy, whose long sideburns blew in the wind, drew a sword from his back and narrowed his eyes. He gave his horse a pat on the rump as a gesture for her to move out of the way. As soon as he ensured she was safe, he attacked the sirens at the same time.
You're losing tension by over-explaining. "As a gesture for her to move out of the way" we get it, he's telling the horse to scram. Trust your reader. Also, "attacked the sirens at the same time" is clunky. Attacked them when? All at once?
Try this: Two shadows a boy and his horse stood frozen at the water's edge, watching the beasts slice through the waves. The boy, maybe eighteen, had sideburns long enough to whip in the wind. He slid a sword from his back, eyes locked on the target. He slapped his horse's rump. Hard. She knew that signal. She bolted for the trees. Only when he heard her hooves hit the dry sand did he turn and charge straight into the pack.
The boy slashed them with his sword and rolled out of the way when four more flew toward him from each direction. They ended up crashing into one another and falling onto the sand.
With his sword still drawn, the boy sprinted down the beach and whistled for his horse.
She leaped out of the jungle and cantered toward him.
Two more watery sirens appeared beside the boy, but he slashed them before they dragged him into the ocean.
His horse soon cantered beside him and gestured for him to jump on.
Her rider put his sword up and grabbed her reins. He leaped onto her back and kicked her sides. “Go! Go! Go!” he yelled in a Scottish accent.
His horse jumped into a gallop and leaped into the jungle again. They left nothing but the sirens’ remains behind.
This whole action sequence is the heart of the chapter, but it reads like a bullet-point list. Action needs rhythm. Short, punchy sentences for impact. Longer ones for breath. Right now, it's all the same length.
Try this: He slashed, he rolled. Sand sprayed. Four more came at him from every angle too fast but they were dumber than they looked. They collided mid-air and hit the ground in a heap.
He didn't wait. He ran.
His whistle cut through the chaos.
She burst from the jungle, sand flying from her hooves, and met him stride for stride. Two sirens lunged from the surf. He spun, sword singing, and they dissolved before they could touch him.
The horse pulled alongside, her body an open invitation. He sheathed his sword mid-stride, grabbed a fistful of mane, and vaulted onto her back. His heels dug in.
"Go! Go! GO!" The Scottish accent tore out of him, raw and desperate.
She launched forward like she'd been shot from a bow, and they plunged into the jungle's darkness, leaving nothing but scattered puddles and the stink of salt behind.
The boy and his horse galloped through the dark jungle, ducking under tree branches.
The boy leaned forward in a two-point position and leaped over a log. He checked behind him to ensure the sirens weren't following, but quickly looked ahead again.
His horse, unfortunately, tripped over a tree root, and she and her rider fell, but without screams. They landed under an open gap in the jungle's treetops.
The moon's rays showered on them, revealing their characteristics. The horse was a beautiful Palomino, and her rider was a handsome, bright-eyed young man who looked to be around eighteen. He wore a medieval-style tunic, a khaki shirt, gray pants, and brown shoes. On his back were a sword case and a shield.
The young man pushed himself up and crawled to his horse. “Are ya all right?” he asked her.
His horse nodded and stood. She shook out her body and quickly turned toward the dark jungle.
Her rider, now covered in dirt, rested his palm on her side. “Don’t worry. I think we’re safe now.” He stood as well and prepared to mount her again.
Again, you're telling me what they look like in the middle of a tense moment. It kills the pace. Sprinkle that stuff in earlier or later. Also, "without screams" is weird. Just say they went down hard and silent that's more badass.
Try this: They tore through the jungle, ducking branches, jumping roots. He rode low against her neck, trusting her eyes more than his own. He glanced back nothing then whipped his head forward.
Too late.
Her front leg caught a root, and the world flipped. They hit the ground like a sack of rocks, no sound but the thud of flesh and the rattle of gear. They slid to a stop in a clearing where the moon broke through the canopy like a spotlight.
For a second, neither moved.
Then the boy groaned and pushed himself up. "Bloody hell..." He crawled to her, hands running down her legs. "Ya all right, girl?"
She snorted, rolled to her feet, and shook from nose to tail. Her ears swiveled toward the dark trees, alert.
He put a hand on her trembling side. "Easy. I think we lost 'em." He was covered in dirt, his tunic torn at the shoulder. Moonlight caught his facesharp cheekbones, bright eyes, maybe eighteen. A Palomino horse and a kid in a medieval tunic, standing in a jungle clearing like they'd fallen out of time.
Before he could, though, a bright, purple light appeared before him, and the boy’s jaw dropped. “Master.” He held his arms out to his sides and stepped back.
From the light, a female voice spoke. “Go, my young apprentice. You must start your journey for the two fairies. They are the Magic and Human Worlds’ only hope for survival against the Octopus Man the only ones who can prevent a calamity.”
“I understand,” the boy replied. “All this training for the past month... It is time to put it into action, Master. Special Spells will help the two fairies win their battle.”
“And remember,” continued the voice, “your sister and I will be with you during your entire mission. You are not alone. Now go.”
Bobbing his head, her apprentice jumped onto his horse again and gave her another kick.
He rode her to the tip of the island’s longest beach, where his Fiji-like house was, as well as a volleyball court and a few beach chairs. Dismounting her, the young man hurried inside his home and grabbed a bag. He dropped to his knees, opened it, and collected some food and water. He put them in the bag, along with a few weapons. He replaced the sword in his sword case that he used to fight the sirens with another sword, a crusader.
When the young man zipped up his bag, he looked up, and his bright eyes landed on his master standing in the front doorway. She only appeared as a sparkling, purple figure because she wasn’t there with him, but he could still make out her eyes and touch her.
Her apprentice threw the strap of his bag over his shoulder and approached her. They shared a goodbye hug, and the young man grasped his master’s hands.
He smiled at her, and she smiled back. She watched as the boy hopped onto the beach and hugged his horse goodbye.
She rubbed her forehead on his side and closed her eyes.
After exchanging goodbye hugs, the boy approached the island’s tip. As soon as he did, he drew his new sword and pointed it at the moon. Its blade glowed, and green magic outlined him.
The boy’s feet lifted off the ground, and it wasn’t long until he floated in midair, staring at the horizon. This was it. The mission would decide whether or not the Human and Magic Worlds would fall.
Turning his head, the young man waved to his master and horse, and they waved back his master with her hand, and his horse with her mane.
Then just like that, the boy shot forward and vanished into the black night.
The ending is solid, but it's rushed. The goodbye with the master and the horse should hurt. Make me feel the weight of him leaving them. Also, "Fiji-like house" and "volleyball court" are jarring. You've built this medieval/fantasy vibe, and then suddenly it's a resort. Commit to one world or make the contrast mean something.
Overall Gut Check:What's working: The bond with the horse is your secret weapon. That's real emotion. The action is relentless. The Octopus Man and the two fairies are intriguing.
What needs work: Point of View. Pick one. Is this the boy's story? Then be in his head. Feel his fear, his confusion, his determination. Right now, I'm watching him from a distance. Get closer.
Pacing: The fight scene is good, but it needs rhythm. Vary your sentence length. The middle section (after the fall) drags because you're info-dumping his outfit and the house setup.
Grammar/Line Edits: It's clean. No major screw-ups. A few clunky phrases ("as a gesture for her to move out of the way"), but nothing that ruins it.
Bottom line: You've got a story here. Now stop reporting it and start living in it. Get dirty. Get scared. Get sad when he says goodbye. Make me feel it.